Circuit breakers



March 12, 1963 M. F. KOENIG ETAL 3,081,386

CIRCUIT BREAKERS Filed Jan. 7, 1960 6 Sheets-Sheet 1 March 12, 1963 M. F. KOENIG ETAL 3,

CIRCUIT BREAKERS Filed Jan. 7, 1960 6 Sheets-Sheet 2 IIIJ'III I Lil-m March 12, 1963 M. F. KOENIG ETAL 3,031,336

CIRCUIT BREAKERS Filed Jan. 7, 1960 6 Sheets-Sheet 3 March 12, 1963 M. F. KOENIG ETAL 3,081,386

CIRCUIT BREAKERS Filed Jan. 7, 1960 6 Sheets-Sheet 4 Izzf as mw wfm' 3% Q0 w. m "Ma "45 8 A 4 March 12, 1963 M. F. KDENIG ETAL 3,081,336

CIRCUIT BREAKERS Filed Jan. 7, 1960 6 Sheets-Sheet 6 5 vx hvgain' x2:;@mv%f8 W "S\ Q. w m. 4. M

United States Patent 3,081,386 CIRCUH BREAKERS Martin F. Koenig and Alexander J. Pastene, Milwaukee,

and Lloyd D. Williams, Waukesha, Wis., assignors to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Filed Jan. 7, 1966, Ser. No. 1,073 34 Claims. (Cl. 290-88) This invention relates to circuit breakers and more particularly to circuit interrupters which are manually operable to close and open a circuit and are automatically oeprable from the closed position to open the circuit in response to abnormal conditions in the electrical circuit.

While not limited thereto, the invention is especially applicable, in addition to its use as a switch for manually closing and opening circuits, to protection of lighting and power circuits and the like from continuous abnormal thermal conditions and from abnormal current overload conditions.

A general object of the invention is to provide an improved circuit interrupter of the aforementioned type.

A more specific object of the invention is to provide improved mechanism for a circuit breaker of the thermal and magnetic trip type.

Another object of the invention is to provide a circuit breaker of the aforementioned type which has a manually operable handle for closing and opening the same and which is provided with improved mechanism permitting the breaker to trip free of the handle so that the breaker cannot be maintained closed against an abnormal circuit condition if the handle is held in its closed position but which moves the handle to open circuit indicating position when it is released.

Another object of the invention is to provide an improved latch mechanism for a circuit breaker to facilitate tripping thereof under abnormal conditions.

Another object of the invention is to provide a circuit breaker with improved means for automatically resetting the operating mechanism following tripping thereof so that the operating handle need only be moved to on position -to reclose the contacts.

Another object of the invention is to provide a circuit breaker of the aforementioned type with an improved latch and latch lever mechanism providing an unstable system.

Another object of the invention is to provide a compensating member for novel cooperation with the aforementioned latch to alter the operation of the latter to compensate for ambient temperature changes.

Another object of the invention is to provide in a circuit breaker a combined thermally and magnetically responsive mechanism of improved type.

Another object of the invention is to provide the aforementioned circuit breaker with improved means for loading the thermally responsive member or for biasing the latter and the magnetically responsive member toward their normal positions.

Another object of the invention is to provide an improved tripping mechanism for a circuit breaker having an overcenter spring for snap-action opening of the confacts, the spring being provided with a predetermined minimum length to permit automatic resetting of the mechanism as aforementioned.

Another object of the invention is to provide a plural-pole circuit breaker comprised of a plurality of single pole circuit breakers each being provided with an internal tripping device of novel construction and the tripping devices being coupled to one another when the breakers are stacked for operation in unison to trip the plurality of poles thereof upon the occurrence of an abnormal condition in the circuit of one pole thereof.

3,081,386 Patented Mar. 12, 1963 Another object of the invention is to provide a novel handle tie for a pair of circuit breakers arranged. in abutting relation and having lost motion for actuating one of the breakers to its open position upon tripping of the other breaker in response to an abnormal condition.

Other objects and advantages of the invention will hereinafter appear.

While the apparatus hereinafter described is efiectively adapted to fulfill the objects stated, it is to be understood that we do not intend to confine our invention to the particular preferred embodiments of circuit interrupters, disclosed, inasmuch as they are susceptible of various modifications without departing from the scope of the appended claims.

The invention will now be described in detail with reference to the accompanying drawings wherein:

FIGURE 1 is an isometric view of a single pole circuit breaker showing the outer configuration thereof;

FIG. 2 is a side elevation view of the breaker of FIG. 1 with the cover removed showing the breaker mechanism in its on position;

FIG. 3 is a side elevation view similar to FIG. 2 show ing the breaker in its off or tripped position;

FIG. 4 is a lateral sectional view taken along line 4-4 of FIG. 2;

H6. 5 is an exploded isometric view of the breaker of FIGS. 1-4 showing the structural parts thereof;

FIG. 6 is an isometric view of the cover of the breaker of FIGS. 15 showing the molded internal structure thereof;

FIG. 7 is a fragmentary side elevation view of the breaker of FIGS. 1-6 showing the breaker parts in the position they assume after tripping but before automatic resetting of the latch lever;

FIG. 8 is a fragmentary side elevation view of a plural pole breaker with the cover of one pole thereof removed showing the breaker in its on position, and showing in dotted lines the latch lever in a tripping position;

FIG. 9 is an isometric view of a common trip lever;

FIG. 10 is a fragmentary side elevation view of a double pole breaker showing the operating handles partly in section and one modification of a handle tie;

FIG. 11 is a fragmentary side elevation view similar to FIG. 8 showing the breaker in its tripped-free-of-the handle position;

FIG. 12 is a fragmentary side elevation view of two single pole breakers in abutting relation showing the operating handles partly in section and a second modification of a handle tie; and

FIG. 13 is a fragmentary top view of the breakers of FIG. 12 showing the operating handles partly in section and showing the handle of one breaker in a tripping position.

Referring to FIG. 1, there is shown a single pole circuit breaker having a shallow insulating housing 2 with its open side closed by an insulating cover 4. The cover is rigidly secured to the housing by a plurality of rivets 6 or the like. Housing 2 and cover 4 are provided at the top portion of the breaker with cut-out portions 10 and 1.2 in registration forming a rectangular opening for accommodating an operating handle 8 which extends to the exterior of the breaker. Handle 8 is provided with a rectangular opening 14 therethrough for receiving a handle tie as hereinafter more fully described. A contact clip 16 extends eXteriorly of the breaker through an opening at the left-hand bottom portion thereof to form one electrical connection thereto as hereinafter described.

As shown in FIG. 2, the breaker is provided with the aforementioned operating handle 8 and a latch 18 pivotally supported thereon and suspended therefrom. A latch lever 20 of substantially inverted U-shaped configuration is arranged for cooperation with latch 18 eration to turn the breaker on and off.

to maintain the breaker in its closed condition. The

lower end of the depending left-hand leg of latch lever and a'projection 24 integral with housing 2 for biasing the latch lever in the counterclockwise direction. A movable contact member 26 is pivotally supported at the upper end thereof on the lower portion of operating handle 8. The lower end of contact member 26 is connected to the mid-portion of latch lever 2t through a helical oyercenter tension spring 28. Overcenter tension spring 28 is provided with a predetermined minimum length to afford resetting of the latch and latch lever after the breaker has been tripped as hereinafter described. Spring 28 is constructed so that at its shortest length each turn-thereof remains under a small amount of torsion thereby to positively cause constriction of the spring to its shortest length when the breaker is tripped. A stationary contact 30 which is integral with contact clip 16 is accommodated in a slot in housing 2 for cooperation with movable contact member 26. One or more flexible electrical conductors 32 are electrically connected at one end thereof to movable contact member 26 and at the other end thereof to a bimetal member 34 adjacent the lower end of the latter. A terminal bracket 36 is rigidly and electrically connected at one end thereof to the upper end of bimetal member 34 and extends therefrom to the exterior of housing. 2. The outer end of terminal bracket 36 is provided with an electrical connector hereinafter described for securing an electrical conductor thereto to form the second connection to the circuit breaker. I e

A magnetic pole piece 38 is pivotally supported at its upper end on opposed projections on the housing and cover hereinafter described. Pole piece 38 is provided at its mid-portion with a substantially longitudinal U- shaped' portion surrounding bimetal member 34 on three sides of the latter. The current flowing in bimetal member 34 energizes the magnetic pole piece and the elongated ends ofthe legs of the U-shaped portion form magnetic poles for attracting an armature. Armature 40 is pivoted at its upper end in suitable alined cavities in base 2 and cover 4 hereinafter described. Armature 49 extends downwardly from its pivot alongside magnetic pole piece 38 andis normally spaced therefrom for attraction by. the latter. A metallic member 42 is rigidly secured adjacent the lower end of armature 40. Member 42. is bent so that its free end diverges from armature 40 into engagement with the lower end of latch 18 to maintain engagement between the lower end of latch 18 and a suitable catch on latch lever Ztl, hereinafter described. While metallic member 42 is preferably a bimetallic member for altering the operation of the breaker to compensate for ambient temperature changes, it will be understood that it mayalso comprise a single rigid piece of material fixed to armature 40 if compensation is not required. A slide plate 44, more clearly shown in FIG. 5, is slidably received in suitable slots in base 2 and cover 4- and is biased in the lefthand direction as seen in FIG. 2 by a helical compression spring '46 positioned between the slide plate and an abutting wall of the housing. Slide plate 44 is provided at its left-hand end with suitable cut-out portions hereinafter described for receiving the reduced end portions of bimetal member 34 and armature 40 in spaced apart relation.

Turning now to the exploded view of FIG. 5, the individual mechanical parts of the circuit breaker willbe described in more detail. Operatinghandle 8 is providedwith a generally rectangular projection 8a which extends ext eriorly of the circuit breaker housing through the opening defined by cut-out portions and 12 for manual op- The central portion of the handle 8 diverges downwardly into a substantially semi-cylindrical portion 8b to maintain the opening in the housing closed throughout the rotation'of the handle. The axis of rotation of suchsemi-cylindrical parallel enlarged portions are provided at the right-hand.

portion is provided with a pair of projections 8c extending in opposite directions laterally of the operating handle for pivoting the latter in the housing and cover. The lower portion of handle 8' is bifurcated into a pair of parallel enlarged portions 8d, the upper surfaces of which stop against the inner surfaces of the housing when the operating handle is rotated and such parallel portions being; spaced in the direction of the aforementioned axis. These sides thereof with alined holes. 89 for receiving the outwardly bent leg portions 18a of a substantially U-shaped latch 18 and pivotally supporting the latter on the operating handle. The yoke portion 18b of latch 18 is flattened into a substantially rectangular cross-section and the upper surface thereof is formed at a predetermined. downward slopetoward latch lever and at a small downward angle from a plane normal to the plane of the latch.

' This downward angle, more clearly shown in FIG. 7, is

sufiicien't to atford an unstable system. Thus, the sloped toward one another, inserting such ends between the spaced portions 8d of the handle and allowing outwardly bent portions 18:: of latchlfi to spring into holes 8e.

The lower left-hand portions of spaced portions 8d of the operating handle are provided with alined holes 8;

for pivotally supporting movable contact member 26.

Movable contact member 26 is provided at its upper end with bifurcated portions having outwardly bent portions- 26'a at the free ends thereof which may be squeezed toward one another and allowed to spring into holes 8 in the operating handle to pivotally support the movable contact member on the handle. The movable contact member 26 is provided with a contact tip 26b for cooperation with the stationary contact as seen in FIG. 2. and is also provided with an aperture 26c in the lateral portion at its lower end for receiving the lower end hook of overcenter tension spring 28. i The latch lever 20 is provided at its mid-portion with an aperture Ztla for receiving the upper-end book of spring 28. The left-hand depending leg of latch lever 26* is provided at its end with a zigzag portion 2% forming a pivot for the latch lever. This zigzag portion of the latch lever is accommodated'in a larger complementary slot 48 in base 2. This type of pivot for the latch lever is preferred over a, pin and aperture type pivot in order to be able to use a latch lever which is narrow at this portion and yet has substantial strength. Immediately adjacent the zigzag portion 2012, the latch lever is provided with an aperture 290 for receiving one end hook of resetting spring 22.. The other end hook of spring 22 encircles projection 24- in the base as seen in FIG. 2.

The outer edge of the right-hand depending leg of latch lever 20 is providedgwith a catch 26d which is spaced from the free endof such leg for engagement with the aforementioned downwardly-angled yoke surface of latch 18.

Stationary contact 30 is of a generally horizontal U- shaped configuration having two spaced depending contact clip portions 16. The yoke of the U-shaped portion is provided with a contact tip 30a, as shown in FIG. 2, for cooperation with contact tip 26b of movable contact member 26. Bimetal member 34,has a longitudinal ribhon-like configuration and a. reduced portion 34:: at its free end. The other end of bimetal member 34 is rigidly secured as by welding to one end of. terminal bracket 36. Adjacent this end, terminal bracket 36 is provided with an offset 36a so that it will clear the pivot portion of magnetic pole piece 38 as shown in FIG. 2. Terminal bracket 36 extends to the exterior of the housing through an aperture therein at the righthand side thereof and is provided at its outer end with a rectangularly bent portion 36b having a threaded aperture 36c therein for receivinga conductor retaining screw 36d. Terminal bracket 36 is provided intermediate its ends with a threaded aperture 36a for receiving an adjusting screw 36 as shown in FIG. 2. The vertical sides of connector portion 3612 are provided with alined apertures 36g having substantially V-shaped lower portions for receiving the end of an electrical conductor.

Magnetic pole piece 38 has a substantially longitudinal U-shaped configuration to surround bimetal member 3-4 on three sides, and is provided at one end integrally therewith with a pair of spaced substantially circular portions 38a. These circular portions are provided with alined oval apertures 38b for receiving opposed projections in housing 2 and cover 4 for pivotally supporting the magnetic pole piece within the housing. These oval apertures 38b allow restricted lateral movement of magnetic pole piece 38 on its pivot projections 64 and 64- to properly orient the pole piece relative to armature 40 under the force of its magnetic field. The other end 330 of magnetic pole piece 38 is bent at right angles thereto and is provided with a laterally extending projection 38d for engaging a molded projection in housing 2 to limit the clockwise pivotal movement of the pole piece.

Armature 40 is provided with a T-shaped end portion 40a, the extremities of the cross on the T being received in suitable alined cavities in base 2 and cover 4 for pivotally supporting the armature. The central portion of armature 40 has an enlarged fiat configuration for cooperation with the pair of poles of magnetic pole piece 33. The other end of armature 40 is provided with a reduced end portion 40b for cooperation with slide plate 44 as hereinafter described. Compensating bimetal member 4-2 is a flat ribbon-like strip having one end bent at a small angle relative to the remainder thereof and the bent end being rigidly secured as by welding to armature 4t} adjacent the reduced end portion 40b thereof.

Slide plate 44 is of generally rectangular configuration having a pair of spaced notches 44a at one end thereof for receiving one end of compression spring 46, the tongue between the notches extending axially inside the spring. The other end of spring 46 is received in a suitable slot 50 in the wall of housing 2 to be retained therein by cover 4. The other end of slide plate 44 is provided centrally thereof with a stepped cut-out portion formed by a relatively wide slot 44!) and a relatively narrow slot 44c extending deeper therefrom. In assembled relation, slot 440 receives reduced end portion 34a of bimetal member 34 and reduced end portion ltlb of armature 40 rests on the shoulders between slots 44c and 44b.

Housing member 2 is preferably of molded insulating material and has molded therein a plurality of walls, projections, cavities and openings for accommodating the mechanical parts hereinbefore described. Thus, housing 2 is provided with a large central cavity 52 'for receiving the movable parts of the breaker and a slightly raised portion 53, also shown in FIG. 4, having a substantially circular depression 54 for receiving one of the pivot projections 80 of operating handle 8. An inwardly extending wall 56 is provided at the lower portion of housing 2 extending partially into cavity 52, the end of such wall serving as a stop for latch lever 20 when the breaker is tripped and the right-hand side of such wall serving to confine slide plate 44. A cavity 58 terminating in an opening 59 at the left-hand bottom portion of housing 2 is provided for receiving stationary contact 30 and for permitting contact clips 16 to extend to the exterior of the housing. A reduced wall 60 extends into cavity 52 from wall 56 to serve as a stop for the counterclockwise pivotal movement of movable contact member 26 and a raised cam portion 61 is provided adjacent such reduced wall to space movable contact member 26 from the base when the contact member opens. A stepped projection 62 is provided substantially centrally of cavity 52. The higher portion 62a of projection 62 serves as a guide for latch lever 20. The rounded side of reduced portion 62b of projection 62 is provided to engage one side of the 6 mid-portion of movable contact member 26 whereon the latter pivots upon opening to assist in moving the operating handle to its off position when the contract opens; yet reduced portion 62b is suificiently short to clear over-center spring 28. Stepped projection 64 having a circular reduced end portion is provided for pivoting magnetic pole piece 38, a similar projection being provided in alinement on the cover 4 as hereinatter described. The internal edge of the upper side of housing 2 is provided with a suitable cavity 66 for receiving one extremity of the T-shaped portion 49a of armature 40 and pivoting the latter therein. Cavity 66 has the configuration of a small segment of an annulus, the deep end of which is closed by a semi-cylindrical portion 66a molded in the housing for retaining one extremity of the T-shaped portion illa of armature ii); and the remainder of the constricted portion of cavity 66 is open for freely accommodating the shank of such T-shaped portion. A number of internal ribs and grooves 68 are provided in the arc chamber for purposes W611 known in the ar-t. A longitudinal passageway 70 extends from the arc chamber along the lower portion of the housing and opens to the atmosphere at the lower right-hand side portion thereof for purposes well known in the circuit breaker art. A groove 72 and a projection 74 are provided adja cent the right-hand wall of housing 2 for securely retaining terminal bracket 36, the end of wall 74 engaging the extreme end pontion of terminal bracket 36 to retain the latter in the adjusted position. A stepped slot 76 is provided in therighthand wall of housing 2 for receiving the aforementioned adjusting screw 36], which threads into the terminal bracket. A projection 78 is provided at the lower right-hand portion of cavity 52 for engaging laterally extending projection 380? to limit the movement of magnetic pole piece 38 toward the armature. An insulating member 80 bent into a right angle is provided for insulating the contacts from the latch lever at its pivot portion. Insulating member 89 is provided with notch 89a for receiving one fo the ribs in the arc chamber to retain the insulating member in its place.

A longitudinal horizontal groove 82 is provided in the lower right-hand portion of the housing for slidably accommodating slide plate 44. This groove extends along the bottom of and through spring receiving cavity 50 in the right-hand wall of the housing. Such extension of groove 82 permits sliding movement of slide plate 44 in the right-hand direction under operating conditions hereinafter described. The left and right walls 10a and 10b of the rectangular opening formed by cut-out portion 10 in the upper portion of the housing diverge outwardly to accommodate rectangular portion 8a of handle 8 in its on and oil positions, respectively. These diverging walls extend from substantially reentrant segmental circular walls and 10d, respectively, forming closely alined surfaces for semi-cylindrical portion 8b of the operating handle as more clearly shown in FIG. 2,.

As shown in FIGS. 2 and 5, the outer side of the righthand wall of the housing is provided with a large cavity 86 at a small angle to the right from the vertical and opening upwardly. The rear wall of this cavity is provided with a substantially rectangular projection (not shown) similar to projection 88 in cover 4 shown in FIG. 6 and in alinement therewith for receipt of rectangular portion 36b of terminal bracket 36 to retain the latter in its place. The right-hand side of cavity 86 is partially closed by an inwardly extending flange 9% having an arcuate slot 92 in alinement with apertures 36g in con nector 36b to facilitate insertion of the electrical conductor. The left-hand wall of cavity 86 is provided with a shallow rectangular depression 94 overlying adjusting screw 36 and its slot 76. Depression 94 terminates at its far edge in a narrow groove 94a the upper right-hand edge 94b of which is at a small angle to the right forming an entrance fora rating card 96. The upper edge of depression 94 is defined by a saw-tooth shaped, do-wn-. I

wardly extending projection 940 for preventing removal ing 98 into the housing through which terminal bracket 36 extends. 7

Referring to FIG. 6, it will be seen that the inner surface of cover 4 is provided with a molded configuration substantially complemental to that of the housing hereinbefore described but of shallower depth. Reference characters similar to those employed to identity the parts of the housing with a prime added identify the pertinent parts of the cover. Thus, cover 4 is provided with a large central cavity 52 and a slightly raised portion 53' having a circular depression 54' for receiving the other pivot projection 8c of the operating handle, also shown in FIG. 4. Slightly raised portions 53 and 53 form guiding surfaces for the operating handle.

of the housing is provided for limiting the opening movement of contact member 26 when the circuit breaker is tripped. A shallow cavity 53' terminating in an opening 59' at the right-hand bottom portion of cover 4 receives stationary contact 3t) and permits contact clip 16 to extend to the exterior of the housing. A stepped projection 64 havinga circular reduced end portion in registration with projection -64 in the housing is provided for pivotally supporting magnetic pole piece 38, these projections being received in aperturesSSb shown in FIG. 5. The internaledge of the upper side of cover 4 is providedwith a cavity 66 similar in configuration to cavity 66 in the housing and having its constricted side substantially closed by a semi-circular molded portion 66a for supporting for free pivotal movement the other extremity of the T-Uhaped portion 49a of armature 4h.

The are chamber portion of the cover is provided with; internal ribs and grooves -68 substantially corresponding to those in the housing and a longitudinal passageway 70 extending from the arc chamber along the lower portion of the cover and opening to the atmosphere at the;

lower left-hand side portion of the cover, passageway 79' being in registration with passageway 79 in the housing.

A groove "72' in registration with groove 72 in the housing is provided for retaining terminal bracket 36. A projection 1th is provided for receipt partway into slot '76 in the housing for maintaining the cover in alinement with the housing, projection 1G0 being smaller than slot 76 to permit limited relative movement to aline-the rivet holes in the cover and housing. A projection 182 is provided at the lower left-hand portion of the cover for abutting the edge of bent end 380 of magnetic pole piece 33 to maintain lateral projection 3812' in interlocking engagement with projection 78 in the housing. Projection 103 in the right-hand portion of the cover is provided for maintaining pivot portion 29b of latch lever 20 in,

slot 48 in the housing.

Cover 4 is provided with a corresponding slide plate groove 82 extending partway into a wall 1%, the latter.

projection 88 and a partial wall 90' having an arouate, slot 90a therein complemental to the corresponding parts.

appearing in the housing.

The operation of a single pole circuit breaker show in FIGS. 1 through 7 will now be described. FIG. 3

shows the position that the circuit breaker mechanism An inwardly extending wall oil in registration with wall 6' tripped. Let it be assumed that the breaker is inthe of wall 659' in the cover as it pivots on the operating han v dle, This causes over-center spring 2-Sto pivot latch lever 20 clockwise effecting stretching of resetting spring 22. As the latch lever pivots in slot 48, the movement of the handle also lifts latch 15 until the yoke'portion 18b of latch 13; engages catch Ziid on the latch lever. 7 Further movement of the handle causes latch 18 to reverse the pivotal movement of latch lever 20 to the counter-clockwise direction, latch lfi being maintained in engagement with catch 2M by the bimetal member 42 bearing thereagainst under the force of compression spring 46. Overcenter spring 28 stretches and the tension in resetting spring 22 is relieved. During this time, the pivot point, namely, holes 8 of movable contact member 26 moves to the right and the upper pivot point, namely, aperture 2%, ofover-center spring 28 shifts to the left. When the mechanism passes the dead-center position wherein movable contact member 26 and over-center spring 28 are in alinement, the movable contact member snaps into abutting engagement with stationary contact tip 30a under the force of over-center tension spring 28 as shown in FIG. 2. In the on position, the right-hand upper edge of the enlarged portion id of the operating handle abuts againstthe inner side of the upperwall of housing 2 and the mechanism is held in this position by spring 28 being under tension and substantially over center position.

It will be apparent from FIG. 2 that in this positionwhen the contacts are closed and the operating handle is in its extreme counter-clockwise position, over-center spring 28 applies its maximum force. This is due to the fact that, following closure of the contacts just beyond the dead-center position, movement of the operating handle to its extreme counter-clockwise position causes counter-clockwise pivoting of latch lever 20 to maintain the tension in spring 23 at its maximum value. Thus, the maximum power of spring 28 is utilized to apply a force on the closed contacts. This is a distinct advantage over known breakers whereinthe overcenter spring is stretched. to its maximum length at the dead center posh tion and decreases in length when the contacts close.

assumes when it is manually turned to its off position,

by turning operating handle 3 the full extent in the clockwise direction. This is also the position that the circuit breaker mechanism assumes after it has electrically.

To turn the breaker to its off position, handle 8 is moved in the clockwise direction. When spring 28 and contact member 26 pass through the dead center position, the latter snapsopen into abutting engagement with walls 6-0 and 6h whereafter the breaker mechanism assumes the position shown in FIG; 3 under the the force of overcenter spring 23. It will be apparent that in this positionthe operating handle is maintained in its extreme clockwise position.

Let it be assumed that thebreaker is in-its on position shown in FIG. 2 and that it is electrically tripped to its off or open contact position in response to an abnormal thermal condition caused by excessive and continuous current flow in the circuit therethrough. This circuit. may be traced from contact clip 1.6,which is normally connected to the power supply line, through stationary contact 30 and its contact tip Sim, contact tip 26!) and movable contact member 26, conductors 32, bimetal member 34 and terminal bracket 36 to connector 36b, the latter being normally connected to a load. Heating of bimetal member 34 due to current flowing continuously therethrough causes bending or flexing thereof so that the free end of bimetal member 34 moves. in the.

right-hand direction. Reduced end portion 34a of bimetal member 34 which is in slot 44c (FIG. 5) of slide plate i i causes sliding of the'latter along groove 82 in the right-hand direction, to further compress spring 4 6. -At this point, it should be noted that spring as. is normally under compression when no current llows in bimetal memher 34 and acts through slide plate 44 to maintain the lower reduced end itlb of armature 4% in its clockwise position wherein the upper end of compensating bimetal member 41 is in engagement with latch 18. 'In this condition, the lower reduced end 34a of bimetal member 34 is free from the bottom of slot 440 of slide plate 44. When normal current, that is less than tripping current, flows in bimetal member 34, reduced end 34a of the latter flexes in the right-hand direction to engage the bottom of slot 440 of slide plate 44 md to slide the latter a small amount in the right-hand direction against the force of spring .6; this action, however, being insufficient to trip the breaker. When the current flow in bimetal member 34 increases, additional flexure thereof causes slide plate 46 to slide further in the right-rand direction. This permits the lower reduced end of armature to move in the right-hand direction to relieve the force normally applied by member 42 against latch 18. When excessive current flows for a predetermined period of time determined by adjustment of screw f, the yoke portion 18b of latch 18 slides clear of catch 2630. to trip the breaker to the position shown in FIG. 3,

More specifically, disengagement of latch 18 from catch Ztld of the latch lever occurs in the following manner: It will be recalled that when no current liows in bimetal member 34-, reduced end 34:: thereof is free of the bot tom of slot 400 in the slide plate. Therefore, all of the force exerted by compression spring 46 is applied through armature and compensating bimetal member 42 to latch 18. When bimetal member 34 flexes under current flow and moves slide plate 46 the aforementioned small amount to the right, a portion of this force is taken up by bimetal member 34 and removed from latch 18, the rernainder of such force remaining on latch 13. This causes the inclined yoke portion 18b of latch is to slide on catch Ztld, this action, however, being insufficient to re lease the catch from the latch. Such relative movement of latch 18 on catch Zhd causes a shift of the ratio of the forces applied from spring 46 to latch 28 and bimetal member 34. That is, a greater portion of the total force is again applied to latch 18 and a lesser portion thereof is applied to bimetal member 34. Therefore, bimetal member 34 must flex further to trip the breaker. When bimetal member 34 flexes suiiiciently, latch 13 slides clear of catch Ztid to trip the breaker to the position shown in FIG. 3.

The tripping action occurs as follows: When latch 13 clears catch 20d, over-center spring 28 pivots latch lever 20 in the clockwise direction and the end of the righthand depending leg of latch lever it strikes wall in the housing as shown in FIG. 7. This causes the upper end of spring 28 to move through its dead-center position relative to movable contact member 26 and the latter snaps to its open contact position. One side of the midportion of contact member 26 strikes the rounded side of reduced portion 62b of projection 62 in the housing and the contact member pivots thereon counterclockwise, thereby to kick the operating handle toward its oil position. Such pivoting of latch lever Zil also causes resetting spring 22 to stretch as shown in FIG, 7, resetting spring 22 being overpowered by over-center spring 28. The remaining constriction of spring 28 causes operating handle 8 to pivot clockwise to the intermediate position shown in FIG. 7, if it is not held in the on position, thereby causing the mechanism to move still further overcenter.

The position of the mechanism illustrated in FIG. 7 is an intermediate unstable position following tripping of the breaker but before the latch lever has been automatically reset. It will be noted that in this position catch 20d on the latch lever has dropped below the yoke portion 18b of latch 18 and that the yoke portion of latch 18 must be brought below catch Ztid in order that the operating handle can again be employed to move the breaker to its on position. Also, in this unstable position, the operating handle is free to pivot further in the clockwise direction. As over-center spring 28 is now at its shortest length, resetting spring 22 pivots latch lever 20 back in the counterclockwise direction from the position shown in FIG. 7 to the position shown in FIG. 3. Latch lever 24) carries with it spring 28 and contact member 26 whereby the latter causes the operating handle to pivot to its extreme clockwise position. The aforementioned pivoting of latch lever 20 and operating handle 8 in opposite directions effects movement of catch Ziid upwardly and movement of latch 18 downwardly wherein the yoke portion 13b of the latch is substantially below the catch 29d to reset the mechanism. In this condition, resetting spring 22 is normally under a small amount of tension as shown in FIG. 3 to positively maintain latch 13 engageable with catch 20d and the breaker is ready to be moved to its on position provided bimetal member 34 has cooled.

Let it be assumed that the breaker is in its on position shown in FIG. 2. and that it is magnetically tripped to its 01 or open contact position in response to an abnormal overload current. A high overload current flowing in the aforementioned circuit between contact clip 16 and connector 30b flows through bimetal member 34. Such ovarload current flowing in bimetal member 34 effects energization of magnetic pole piece 38. It will be apparent that pole piece 38 is pivoted at its upper end, as seen in FIG. 2, in the housing and cover and its lower end is restrained from moving to the left by lateral projection 38d extending from right angle portion 38c more clearly shown in FIG. 5. As a result, energized pole piece 38 attracts armature 40' thereto and the lower reduced end 40b moves slide plate 44 along groove 82 in the right-hand direction to compress spring 46. Slide plate 44- is free to move relative to bimetal member 34 an amount determined by the depth of slot 440 in the slide plate shown in FIG. 5, this being sufiicient to cause tripping of the breaker. Armature 40 carries member 42 therewith to relieve the force which maintained engagement of catch 20d and latch 1t; and the latter slides off catch 20d to permit tripping of the breaker as hereinbefore described.

While member 42 may be a single rigid piece of material if temperature compensation is not required, it is preferably a bimetallic member which automatically adjusts the force on latch 18 in response to ambient temperature changes. It will be recalled that heating of the primay bimetal member 34 causes flexure of the lower free end thereof in the right-hand direction. Without compensation, such flexure of member 34 caused by ambient temperature increase would reduce the force on latch 18 to effect tripping of the breaker in response to current values which are lower than the desired values. To prevent this, the free end of compensating bimetal member 42 is arranged to fiex in the left-hand direction in response to such ambient temperature increase to maintain the force of latch 18 substantially constant until current flows in the circuit. Thus, any flexure of member 34 caused solely by ambient temperature change will be taken up by complementary flexure of compensating bimetal member 42 in the opposite direction.

The breaker shown in FIGS. 1 through 7 is constructed so that it can trip free of the operating handle. Let it be assumed that the breaker is in the on position shown in FIG. 2, that the operating handle is physically held in the position shown and that a current is passed through bimetal member 34 to permit latch 18 to disengage catch 2nd on the latch lever. As a result, over-center spring 23 pivots latch lever 20 in the clockwise direction. This pivotal movement of the latch lever causes spring 28 to pass through and beyond its dead-center position relative to movable contact member 26. As spring 28 moves beyond the dead-center position, the right-hand depending leg of latch lever 20 stops against wall 56, whereafter it pivots contact member 26 counterclockwise into abutting ll engagement with projection 62b in the housing. Thus, the contacts are opened and this condition is maintained by remaining tension in spring 28 over-powering resetting spring 22, as illustrated in and more clearly hereinafter described in connection with FIG. 11. When the operating handle isreleased, the remaining tension in spring 28 acting through contact member 26 causes clockwise pivoting of the operating handle to the intermediate position shown in FIG. 7. This action moves the pivot point of the contact member still farther from the point where spring 28 is pivoted on latch lever 2d to maintain the contacts open. As spring 23 constricts to its shortest length, resetting spring 22 resets the mechanism to the position shown in FIG. 3 as hereinbefore described.

The breaker may be adjusted by turning screw 36f. Before rating card 96 is inserted in its place in the housing, turning of screw 38 in will cause flexure of terminal bracket 36 and movement of the lower end of bimetal member itiin theright-hand' direction, as seen in FIG. 2.

This will effect movement of slide plate 44 to the right against the force of spring as. As a result, the breaker will require, a lower thermal condition and a smaller value of overload current to trip the same. Conversely, turning of screw 36f out will permit terminal bracket 36 to relax or straighten from its flexed condition. This will cause movement of the lower end of bimetal member 34 in the left-hand direction whereby member 42 applies a greater force against latch 18 under the action of compression spring 46. As a result, the breaker will require a higher thermal condition and a larger value of overload current to trip the contacts open. After screw 38 has been adjusted as desired, rating card 96 is inserted thereover to prevent change of the rating of the breaker except by forcibly removing such card.

Referring to FIGS. 8, 9, and ll, there is shown a double pole circuit breaker- Reference characters similar to those in the single pole breaker of FIGS. 1 through 7 have been employed for like elements. Each-pole 1% and 108 of the double pole breaker shown in FIG. 10

is similar to the single pole breaker hereinbefore de scribed except that housing 2 and cover 4- have been modified to accommodate the common trip lever shown in FIG. 9. To this end, housing 2' is provided with a round hole 110 and cover 4' is provided with a similar hole (not shown) in registration with hole 110 for pivotally supporting the common triplever.

As shown in FIGS. 8 and 9, common trip lever 112 is provided with a cylindrical portion 114 having one round end 114a thereofjournaled in hole 110 in the'housing and having the other round end 1141) thereof journaled in the aforesaid hole in the cover, these holes forming rotary bearing surfaces for the common trip lever; Each end 114a and 11412 thereof is provided with a transverse slot lldc and 114d'extending across the axis' of cylindrical portion 114 and having a predetermined depthaxially thereof; Each such slot is formed to receive and frictionally engage one-half of a flat, rectangular connecting member 116. The other half of such connecting mem her is received and frictionally engaged in a corresponding slot inthe common trip lever of the adjacent pole of the breaker to rigidly connect such'common trip levers for' rotation in'unison.

Lever 1-12 is composed of suitable insulating material. Cylindrical portion 114 has integrally molded therewith intermediate its ends and along one side thereof an arcuate enlarged portion 118 and alongthe other side. thereof an arcuate enlarged portion 120, the latter having a. projection 122 radially extending therefrom. The arcuate portions 113 and 12tiyare spaced fromtthe ends of lever 112 and form thrust bearing surfaces between lever 112 and the housing and cover. The left-hand side 122a. of projection 122 is formed so thatit diverges radially at a small'angle relative to the-right-hand side 122k a distance approximately one-half the length of the latter side. At

12' this point, side 1220: is formed with a narrow shoulder 122c terminating in an inclined planar cam surface 122d converging toward side 122b, cam surface 122d terminating in a narrow surface 122a substantially normal to side 1221) and connecting with the latter. As more clearly shown in FIG. 8, inclined surface 122d forms a cam surface for causing rotation of the trip lever when struck by latch lever 29, as shown in dotted lines, upon tripping of the breaker. The extremity of side 122/5 is provided with a stepped projection 122 for engaging member 42 as hereinafter described. a

As shown in FIG. 10, operating handles 8 of the double pole breaker comprising poles 1% and 1% are mechanically connected to one another by a handle tie 126. Handle tie 126 is provided intermediate its ends with an enlarged portion 126a having a configuration substantially corresponding to the configurations of the operating handles and filling the space therebetween at their ends. The reduced ends 126b and 1260 of the handle tie are provide with a rectangular cross-section for insertion in and for close fitting engagement in rectangular openings 14 in the operating handles. 7

The operation of thedouble pole circuit breaker will now be described. Let it be assumed that the breaker is in its on position shown in FIG. 8 and that it is tripped, either thermally or magnetically as hereinbefore described in connection with the single pole breaker, to its off or open contact position. Removal of the force from latch 1% permits the latter to slide off catch 20d to release latch lever 20. As a result, over-center spring 28 rotates latch lever 20 clockwise, causing the end of the right-hand depending leg thereof to strike inclined surface 122d of trip lever 112 as shown in dotted lines in FIG. 8. This eitects rotation of trip lever 112 clockwise and latch lever 20 stops against shoulder 1220 of the trip lever as shown in FIG. 11. The clockwise rotation of the trip lever operates through connecting member 116 to effect similar rotation of the trip lever in the adjacent pole of the double pole breaker. As a result, the

upwardly extending projection 122 on the trip leverin the adjacent pole bears against bimetal member 42 and movesthe same and armature itl and slide plate 44 to the right as shown in FIG. 11 to permit release of latch 18 from catch 20d in the adjacent pole to trip the latter. The clockwise rotation of the latch lever in each pole effects movement of spring 28 over center to cause opening of the corresponding contacts. As the handles are connected by tie 126, they are moved in unison to .the'

off position under the pivoting action of contact member 26 on the sideprojection 62b and the action of overcenter spring 28 and resetting spring 22. in each pole of the breaker. The double pole breaker may be reclosed by moving operating handles 3 counterclockwise to their on position. a

The double pole breaker is constructed so that it can trip free of the operating handles. If the operating handles are physically held in their on position as shown in FIG. 11 andthe force normally applied against latch 18 is sufficiently decreased either by thermal or magnetic action or by clockwise rotation of common trip lever 112, latch ls'disengages catchltld 0f latch lever 20. As a result, lever 20 rotates clockwise under the force of spring 28 as shown in FIG. 11. This action .causes the upper pivot of spring 28 to pass through the dead center position relative to contact member 26 to disengage the latter from stationary contact 30.. The breaker mechanism remains in the position shown, in FIG. 11 until operatinghandle 8 is released, whereafter handle 8 is rotated to its off position by springs 28 and ZZJ Spring 22 also resets the latch and latch lever as hereinbefore described to. prepare the breaker for reoperation to its on position.

FIG. 12 shows a double pole breaker formed by arranging two single pole breakers 136i and 132 in abutting relation and connecting their operating handles 8 by a novel functioning lost-motion type of handle tie 134. Each breaker 130 and 132 is similar to the single pole breaker hereinbefore described in connection with FIGS. 1 through 7 and each is provided with a housing 2 and cover 4 and operating handle 8. The operating handle of each breaker is further provided with a rectangular opening 14 more clearly shown in FIG. 7. Handle tie 134 is provided intermediate its ends with an enlarged, substantially cylindrical portion 134a each end of which is beveled to form an abruptly tapered surface 1341). The reduced end portions 134a and 134d are tapered in opposite directions and are inserted into openings 14 in the operating handles of the adjacent breakers. The ends of enlarged portion 134a are beveled to afford lost motion clearance between the same and the opposed sides of the operating handles when one breaker is tripped as shown in FIG. 13. Also, the reduced end portions 134a and 134d are of smaller dimension than the horizontal width of opening 14 to afford lost motion sufiicient to insure opening of breaker 130 in response to tripping of breaker 132.

Let it be assumed that breaker 132 is tripped electrically as shown in FIG. 7. Latch lever 2t) stops against wall 56 and the contacts are opened. Spring 28 having passed through its dead-center position to open the contacts, the tension in spring 28 acting through contact member 26 accelerates operating handle 8 in the clockwise direction. Before the operating handle reaches the position shown in FIG. 7 wherein spring 28 is of shortest length, the lost motion between handle tie 134 and the operating handles of breakers 139 and 132 is taken up as shown in FIG. 13. As a result, handle tie 134 kicks the operating handle of breaker 130 toward its off position. The remaining tension in over-center spring 123 combined with the tension in spring 22 of breaker 132 is sufiicient to cause the operating handle of breaker 130 to be moved beyond the dead-center position of the mechanism therein. Thus, the opening action of breaker 130 will be completed under the action of its own overcenter spring. It will be apparent that whereas one pole of the double pole breaker shown in FIGS. 8 through 11 is stripped in response to tripping of the other pole, one pole of the double pole breaker shown in FIGS. 12 and 13 is turned to its open position in response to tripping of the other pole.

We claim:

1. In a circuit breaker of the type having a circuit breaker operating mechanism for operating the breaker between circuit-closed and circuit-open conditions and an operating lever for actuating said operating mechanism, the improvement comprising an unstable latch means operable on said operating mechanism to maintain the same in circuit-closed condition when a force is applied to said latch means, means operative to provide said applied force to said latch means to maintain said operating mechanism in circuit-closed condition, and means responsive to an abnormal electrical condition for decreasing said force, said latch means being unstable and thereby being automatically operable to release said operating mechanism to allow tripping of the latter to circuit-open condition in response to decrease of said force by a fraction of its total amount.

2. The invention defined in claim 1, wherein said latch means comprises a catch on said operating mechanism, a latch member engaging said catch when a force is applied thereto and having a portion causing automatic disengagement thereof from said catch when said force is decreased.

3. In a circuit breaker of the type having a circuit breaker operating mechanism operable upon the occurrence of a predetermined current in the circuit thereof to open said circuit and trip means operable to maintain said operating mechanism in circuit-closed condition and to release said operating mechanism to allow the same to operate to circuit-open condition and an operating lever for manually moving said operating mechanism between circuit-closed and circuit-open conditions, the improve ment comprising an unstable latch between said trip means and said operating mechanism operable to latch said operating mechanism in circuit-closed condition and to automatically unlatch the same for operation to circuit-open condition upon the occurrence of said predetermined current, said trip means comprising means normally applying a bias force to said latch to maintain said operatin mechanism in circuit-closed condition, and means responsive to said predetermined current for opposing said bias force, and said unstable latch being maintained in latching engagement with said operating mechanism in response to said bias force normally applied thereto and being automatically operable to disengage said operating mechanism when said opposing means decreases said bias force.

4. The invention defined in claim 3, together with another like circuit breaker, an opening in the operating lover of each said breaker, a handle tie having oppositely extending reduced end portions accommodated in the openings in said operating levers to provide partial lost motion connections therebetween, and said lost motion being taken up upon rotation of and acceleration of the operating lever when one of said breakers trips to cause said handle tie to move the operating lever of the other breaker toward its off position regardless of current flow in said other breaker.

5. In a double-pole circuit breaker, two single pole circuit breakers arranged in side by side relation, each said breaker having a housing and an operating handle extending from the housing for turning the breaker between circuit-open and circuit-closed conditions and an electroresponsive trip mechanism for tripping the breaker from circuit-closed to circuit-open condition, an opening in the operating handle of each said breaker, a handle tie having oppositely extending reduced end portions accommodated in the openings in said operating handles to provide lost motion connections therebetween, and said lost motion being taken up upon partial rotation of and acceleration of the operating handle when one of said breakers trips to cause said handle tie to move the ope ating handle of the other breaker toward its circuit-open position regardless of current flow in said other breaker.

6. In a circuit breaker of the type having a circuit breaker operating mechanism operable upon the occurrence of a predetermined current in the circuit thereof to open said circuit and current responsive means operable in response to said predetermined current to trip said operating mechanism to allow the same to operate to circuit-open condition and an operating lever for manually moving said operating mechanism between circuitclosed and circuit-open conditions, the improvement comprising unstable latch means which comprises a catch on said operating mechanism and a latch member pivotally supported on said operating lever at one end thereof and having at its other end a cam surface for engaging said catch, biasing means applying a force to said other end of said latch member to maintain engagement between the latter and said catch thereby to maintain said operating mechanism in its circuit-closed condition, said current responsive means having a portion cooperating with said biasing means and being operable upon the occurrence of said predetermined current to act against said biasing means to decrease the force on said latch member whereby said cam surface slips off said catch to trip said operating mechanism to circuit-open condition.

7. In a circuit breaker, a stationary contact, a movable contact member, an operating lever mounted on a fixed pivot, means pivoting said contact member on said operating lever, a releasable latch lever mounted on a fixed pivot, an overcenter tension spring having one end at tached to said latch lever and the other end attached to said contact member, said latch lever when released causing said overcenter spring to move through its dead center position relative to said contact member to effect automatic disengagement of said contact member from said stationary contact, said contact member when disengaged causing said operating lever to pivot toward its oft position under the force of said overcenter spring, a trip device operable in response to abnormal electrical conditions to release said latch lever, said trip device comprising a latch member normally engaging a catch on said latch lever to maintain the latter in unreleased position, said latch member when released causing release of said latch lever therefrom, and a resetting spring connected between a fixed point and said latch lever for resetting the latter to afford reengagement of said catch and said latch member and for rotating said operating lever all the way to its oil? position to indicate that the breaker has tripped.

8. The invention defined in claim 7, wherein said overcenter spring is provided with a predetermined minimum length to eiiect complete shortening thereof before said operating lever reaches its extreme off position thereby permitting said resetting spring to reset said latch lever without opposing force from said overcenter spring.

9. The invention defined in claim 7, wherein said latch member is provided with a cam surface engaging said catch when a force is applied to said latch member, said cam surface effecting automatic separation of said latch member from said catch when said force is decreased a predetermined amount to form an unstable system.

10. The inventon defined in claim 9, wherein said trip device further comprises biasing means normally applying a force to said latch member in the unreleased position of said latch lever, and means responsive to said abnormal electrical condition for decreasing said force.

11. The invention defined in claim 7, wherein said latch member is pivotally supported on said operating lever for causing reverse movement of said latch lever back to its unreleased position in response to pivotal movement of said operating lever to its on position, said reverse movement of said latch lever efiecting passage of said overcenter spring and movable contact memher through their dead center position to cause reengagement of said movable contact member and said stationary contact.

12. In a, circuit breaker, in combination, an insulating housing, a stationary contact in said housing, a movable contact member, an operating lever ro'tatably mounted in said housing and-having an operating handle extending externally of said housing, means pivoting said contact member on said operating lever, a releasable latch lever pivotally mounted in said housing, an overcenter tension spring having one end attached to said latch lever and the other end attached to said movable contact member, said latch lever when released causing said overcenter spring to move'through its dead center position relative to said. movable contact member under the force of the tension in said overcenter spring to effect automatic. disengagement of said movable contact member from said stationary contact, said contact member when disengaged causing said operating lever to rotate from its extreme counterclockwise on position toward an intermediatev unstableposition short of its extreme clockwise off position under the force of the remaining constriction of said overcenter spring, a trip device operable in response to abnormal electrical conditions to release said latch lever, said trip device comprising a latch member normally, engaging said latch lever to maintain the latter inunreleasedposition, said latch lever when released pivoting relative to said latch member, and a resetting spring connected between said housing and said latch lever operable following complete constriction of said overcenter spring to reset said latch lever to an intermediate position wherein the same is subject to reengagement by said latch member, said latch lever when so reset operating through said overcenter spring and said contact finger to rotate said operating lever to its extreme clockwise off position whereby said breaker is preset for reclosure of the contacts by a single stroke rotation of said operating lever back to its extreme counterclocke wise on position.

13. The invention defined in claim 12, together with another like breaker, each said breaker being provided with a common trip lever rotatably mounted in its housing, said common trip lever having a projection extending therefrom, one side of said projection having a cam surface in the path of a movable portion of said latchlever to cause rotation of said common trip lever when:

said latch lever is released, the other side extremity, of

said projection having a portion acting upon said trip 7 an abnormal electrical condition causes tripping of the other breaker by its common trip lever;

14. In a circuit breaker, in combination, an insulating housing, a stationary contact in said housing, a movable contact member in said housing, an operating lever having a handle portion extending exteriorly of said housing and being rotatably supported in said housing for moving said contact member into and out of engagement with said stationary contact, said contact member being pivotally supported on said operating'lever, a latch lever pivotally supported in said housing, an overcenter spring connected between said latch lever and said contact member, a latch member pivotally supported on said operating lever, a catch on said latch lever for engagement by said latch member to pivot said latch lever in one direction in response to rotation of said operating handle in its on position and for moving said overcenter spring through dead center position relative to said contact member to effect snap action engagement of said stationary contact by said movable contact member under the force of the tension in said overcenter spring, means for biasing said latch member in said catch to maintain engagement therebetween in; said on position, and means responsive to an abnormal electrical condition for acting on said biasing means to allow disengagement of said latch member from saidcatc'h to cause tripping ofsaid contact member out of engagement with said stationary contact and for rotating said operating handle to its off position under the. force of said overcenter spring. a a

15. The invention defined in claim 14, together with another like circuit breaker, the housing of said breakers being in abutting relation, an opening in the externally extending operating handle of each said breaker, a handle tie having oppositely extending reduced end portions accommodated in the openings in said operating handles, said reduced end portions cooperating with said" openings to afford a lost motion connection between the operating handles of said breakers to permit acceleration of the operating handle of'a first breaker toward its off tion to cause said handle tie to move the operating handle of the second breaker off regardless of current flow in' the. latter. 7 a 1 16. In a circuit breaker operable to trip free of its operating handle, a stationary contact, a movable contact member, an operating lever mounted on a fixed pivot and having an operating handle, means pivotally supporting said contact member on said operatinglever, a releasable latch lever mounted on a fixed pivot, an over center tension spring having one end connected to said latch lever and the other end connected to said contact member, means comprising a latch responsive to rotation of said operating handle to its extreme on position for moving said latch lever in a first direction and the 17 pivot of said contact member being simultaneously moved in a second direction against the force of said overcenter spring whereby said overcenter spring and said contact member move through their dead center position to cause said contact member to snap into engagement with said stationary contact, a trip device operable in response to abnormal electrical conditions for releasing said latchto effect release of said latch lever for movement in the opposite direction under the force of said overcenter spring while said operating handle is held in its on position, said latch lever carrying said overcenter spring through said dead center position in the opposite direction to cause said contact member to snap out of engagement with said stationary contact, and means for rotating said operating handle upon release thereof to its extreme off position to afford reengagement ofsaid latch.

17. The invention defined in claim 16, wherein said means comprises a resetting spring connected between said, latch lever and a fixed point, said resetting spring being overpowered by said overcenter spring when the latter moves said latch lever in said opposite direction upon release thereof, said overcenter spring being responsive to release of said operating handle to rotate the latter to an unstable intermediate position wherein said overcenter spring is of minimum length thereby to terminate its opposing force on said resetting spring, said resetting spring being responsive to constriction of said overcenter spring to reset said latch lever in said first direction a distance sufficient to afford reengagement of said latch, and said overcenter spring having a predetermined minimum length under stress whereby said resetting of said latch lever acts therethrough and through said contact member to rotate said operating lever to its extreme off position.

18. The invention defined in claim 17, wherein said latch comprises a catch on said latch lever and a U-shaped member pivotally supported at its free ends on said operating lever, and resetting of said latch lever causes movement of said catch and said U-shaped member toward and beyond one another to afford reengagement thereof when said operating handle is again rotated to its on position.

19. In a circuit breaker, an insulating housing, a stationary contact, a movable contact, an operating handle for moving said movable contact into engagement and disengagement with said stationary contact, said operating handle having enlarged bifurcated portions having alined apertures therein, said movable contact having bifurcated portions pivoted at their ends in said alined apertures, a latch lever pivotally supported in said housing for. movement between the bifurcated portions of said operating handle, an overcenter spring connected between saidmovable contact and said latch lever, means responsive to movement of said operating handle to its on position for moving said latch lever in one direction and for moving said movable contact pivot in another direction thereby to cause said spring to pass through dead center position relative to said movable contact and to actuate the latter into engagement with said stationary contact and for maintaining such engagement when said operating handle is released, said means comprising a catch on said latch lever, a movable latch engaging said catch, and means normally applying a biasing force to said latch to maintain the same in engagement with said catch, and electroresponsive means connected in circuit with said contacts and responsive to an abnormal electrical condition for counteracting said biasing means to afford release of said catch from said latch thereby to effect disengagement of said movable contact from said stationary contact.

20. In a circuit breaker, in combination, an insulating housing, a stationary contact supported in said housing, a movable contact, an operating lever, an overcenter mechanism responsive to movement of said operating lever for moving said movable contact into and out of engagement with said stationary contact, said overcenter mechanism comprising a trip lever having a catch thereon and a latch member engaging said catch and movable with said operating lever when the latter is moved into contact closing position for actuating said overcenter mechanism to effect engagement of said movable contact with said stationary contact, a bimetal member electrically connected to said movable contact, a magnetic pole piece supported in said housing adjacent said bimetal member and energizable by current flow through the latter, a magnetic armature pivotally supported in the housing in spaced relation to said pole piece for attraction by the latter in response to excessive current flow in said bimetal member, biasing means normally applying a force to said armature, said armature having a portion for transmitting said force to maintain engagement of said latch member in said catch, said latch member and said catch being freely separable when said force is reduced, and current flow in said bimetal member causing flexure thereof or attraction of said armature by said pole piece to counteract said biasing force thereby to release said trip lever and to cause said overcenter mechanism to snap said movable contact out of engagement with said stationary contact.

21. The invention defined in claim 20, wherein said portion of said armature which transmits said force comprises a compensating bimetal member operative to compensate for flexure of the first mentioned bimetal member under ambient temperature changes.

22. The invention .defined in claim 20, wherein said magnetic pole piece is pivotally supported at one end in said housing, said pole piece having a U-shaped configuration for surrounding said bimetal member on three sides thereof, the free ends of the legs of said U-shaped pole piece defining air gaps between the same and said armature, and the unsupported end of said pole piece having a. lateral extension for engaging a projection in said housing to limit the pivotal movement of said pole piece toward said armature.

23. The invention defined in claim 20, wherein said biasing means comprises a slide plate slidably mounted in said housing, one end of said slide plate having a notch freely accommodating an end of said bimetal member and a shoulder spaced from the bottom of said notch accommodating the free end of said armature, and a compression spring between the other end of said slide plate and said housing for biasing said armature toward said latch member.

24. In a circuit breaker of the type having a circuit breaker operating mechanism for operating the breaker between circuit-closed and circuit-open conditions and electroresponsive trip means operable to maintain said operating mechanism in circuit-closed condition and further operable upon the occurrence of a predetermined current therein to release said operating mechanism to permit the latter to trip to circuit-open condition and an operating lever for manually moving said operating mechanism between circuit closed and circuit-open conditions, the improvement comprising an unstable latch engaging said operating mechanism to maintain the latter in circuit-closed condition when a force is applied to said latch, and biasing means applying a force to said latch, said biasing means comprising a slidable member and a compression spring biasing said slidable member, said slidable member acting through said trip means to apply a force to said latch.

25. The invention defined in claim 24, wherein said operating mechanism is provided with a catch, and said latch comprises a pivotal member mounted on said operating lever, said pivotal member having a cam surface engaging said catch under the force of said biasing means and being freely slidable therefrom when the force of said biasing means is decreased in response to operation of said trip means.

one end for cooperation with said-pole piece, a compensating bimetal member secured to said armature, and said biasing means acts on the free end of said armature whereby said compensating bimetal member normally maintains engagement of said latch.

27. In a plural pole circuit breaker, in combination, a

plurality of individual circuit breaker units assembled together, each such unit comprising an operating mechanism for operating the breaker unit between circuit-closed and circuit-open conditions, an operating lever for actuating said operating mechanism, latch means maintaining said operating mechanism in circuit-closed condition when a force is applied to said latch means and being automatically operable to trip said operating mechanism to circuit-open condition when said force is decreased, electroresponsive trip means, biasing means acting through said trip means to apply said force to said latch means, and said electroresponsive trip means counteracting said biasing means to decrease said force upon the occurrence of predetermined current, a rotatably mounted common trip member in each said breaker unit operable to rotate in response to tripping movement of the operating mechanism in the associated breaker unit, readily insertable and removable members extending partway into adjacent breakers for connecting said common trip members for rotation in unison, and a projection on each said common trip member, said projections acting on said electroresponsive trip means to trip the remaining breaker units in response to tripping movement of the operating mechanism in any breaker unit.

28. The invention defined in claim 27, wherein said projection on each said common trip member is provided with an inclined cam surface on one side thereof for en gagement by the associated operating mechanism upon tripping of one breaker unit to rotate said common trip members, and the other side extremity of such projection in the other breaker units act against the electroresponsive trip means thereof simultaneously to trip the operating mechanisms of such other breaker units.

29. In a circuit breaker having a stationary contact,

a movable contact member, a pivotally mounted operat ing lever for moving said movable contact member into and out of engagement with said stationary contact, said movable contact member being pivotally mounted on said operating lever, a latch lever supported. on a fixed pivot and an overcenter spring connected between said latch lever and said movable contact member, the improvement comprising means responsive to pivotal movement of said operating lever for causing relative movement of said latch lever and said movable contact member in opposite directions against the tensile force of said overcenter spring thereby to move said overcenter spring through its dead center position relative to said movable contact member to effect snap action engagement of said stationary contact by said movable contact member under the force of the tension in said overcenter spring, said means comprising a member responsive to further pivotal movement of said operating lever after the contacts are closed to cause further movement of said latch lever to maintain the maximum tensile force of said overcenter spring whereby said overcenter spring applies maximum force on the contacts when the latter are closed.

30. The invention defined in claim 29, wherein said means comprises a catch on said latch lever, and the last mentioned member comprises a latch member pivotally mounted on said operating lever, and means for maintaining said latch member in engagement with said catch to move said latch lever when said operating lever is latch member is free to slide ofif said catch when said maintaining means is rendered inefiective, and said maintaining means comprises spring biased means for applying a force on said latch member to normally hold the latter in engagement with said catch.

32. In acircuit breaker of the type having a circuit breaker operating mechanism for'operating the breaker between circuit-closed and circuit-open conditions and an operating 'lever for actuating said'operating mechanism, the improvement comprising:

(a) an unstable latch means operable on said operating mechanism to maintain the same in circuit-closed condition when a force is applied to said 'latch means, said latch means being unstable and thereby being automatically operable to release said operate ing mechanism to allow tripping of the latter to circuit-open condition in response to decrease ofsaid force by a predetermined amount, said latch means comprising; I

(b) a catch on said operating mechanism; a

(c) alatchrnember engaging said catch when a force is applied thereto and having a portion causing automatic disengagement thereof from said catch when said force is decreased. 7

33. In a circuit breaker of the type having acircuit breaker operating mechanism for operating thebreaker between circu'it-closed'and circuit-open conditions and an operating lever for actuating said operating mecha- (0) and said latch means comprising a catch on said releasable member; (d) and a latch member pivotally supported on said operating lever and having a cam surface engaging.

said catch when a force is applied thereto, and said cam surface being operable to slip 01f said catch and release said releasable member when said force is decreased, I v I V 34. In a circuit breaker of the'type having a circuit breaker operating mechanism operable upon the occurrence of a predetermined current in the circuit thereof to open said circuit and trip means operable to maintain said operating mechanism in circuit-closed condition and to release said operating mechanism to allow the same to operate to circuit-open condition and an operating lever for manually moving said operating mechanism between circuit-closed and circuit-open conditions, the improvement comprising:

(a) an unstable latch between said trip means and said operating mechanism operable to latch-said operating mechanism in circuit-closed condition and to automatically unlatch the same for operation to circuit-open condition upon the occurrence of said predetermined current, said unstable latch being maintained in latching engagement with said operating mechanism in response to a bias force normally applied thereto and being automatically operable. to disengage said operating mechanism when said trip means decreases said bias force, said unstable latch comprising:

*(b) a catch on said operating mechanism;

'(c) a latch member pivotally supported on said operating lever at one end and having a cam surface at its other end for engaging said catch and beingfree 21 22 to slip off therefrom when said force on said latch 2,416,163 Dyer et a1. Feb. 18, 1947 member is decreased. 2,703,827 Gelzheiser Mar. 8, 1955 2,798,918 Gelzheiser July 2, 1957 References Cited in the file of this patent 2,889,428 Kingdom et a1. June 2, 1959 UNITED STATES PATENTS 5 FOREIGN PATENTS 2,015,633 Dorfman Sept. 24, 1935 527,827 Canada July 17, 1956 2,403,063 Elmer July 2, 1946 827,740 Great Britain Feb. 10, 1960 

1. IN A CIRCUIT BREAKER OF THE TYPE HAVING A CIRCUIT BREAKER OPERATING MECHANISM FOR OPERATING THE BREAKER BETWEEN CIRCUIT-CLOSED AND CIRCUIT-OPEN CONDITIONS AND AN OPERATING LEVER FOR ACTUATING SAID OPERATING MECHANISM, THE IMPROVEMENT COMPRISING AN UNSTABLE LATCH MEANS OPERABLE ON SAID OPERATING MECHANISM TO MAINTAIN THE SAME IN CIRCUIT-CLOSED CONDITION WHEN A FORCE IS APPLIED TO SAID LATCH MEANS, MEANS OPERATIVE TO PROVIDE SAID APPLIED FORCE TO SAID LATCH MEANS TO MAINTAIN SAID OPERATING MECHANISM IN CIRCUIT-CLOSED CONDITION, AND MEANS RESPONSIVE TO AN ABNORMAL ELECTRICAL CONDITION FOR DECREASING SAID FORCE, SAID LATCH MEANS BEING UNSTABLE AND THEREBY BEING AUTOMATICALLY OPERABLE TO RELEASE SAID OPERATING MECHANISM TO ALLOW TRIPPING OF THE LATTER TO CIR- 